Significant Accounting Policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 1,400,046	$ 1,058,166	$ 3,845,970	$ 2,941,740
LTL Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	1,378,339	1,044,640	3,787,721	2,903,140
Other Service Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from operations	$ 21,707	$ 13,526	$ 58,249	$ 38,600